Amplitude shift keying (ASK) amplitude modulation (AM) is a relatively simple and inexpensive modulation method for sending data via radio. In this approach, a radio frequency (RF) sine wave or “carrier” may be in an on state (e.g., full amplitude), or an off state (e.g., zero or reduced amplitude), depending on whether a respective binary ‘1’ or ‘0’ is to be sent. The duration of each bit may be dependent on a desired transmit spectrum, as well as the robustness of the receiver. However, each bit typically occupies many cycles of the carrier wave. Unfortunately, this conventional approach, while being relatively simple, is also fairly inefficient in terms of both power and radio spectrum usage.
A receiver for such a scheme may simply include an amplifier, a narrowband filter, and a diode peak detector. FIG. 1 shows a conventional demodulator 100 that uses the diode peak detection method. The input signal, which may be a band-pass filtered RF signal or a mixer output intermediate frequency (IF), and as exemplified by the input waveform shown, may be provided to diode detector 102. Diode detector 102 can generate a half-wave rectified version of the input signal at node 112 (see, e.g., waveform 112), an input to buffer 110. Node 112 can also connect to low pass filter 104, which may have a cutoff frequency on the order of a half or quarter of the frequency of the input. Buffer 110 can provide an input to low pass filter 108, which may have a cutoff frequency on the order of several bit times of the ASK modulation. Filter outputs from 104 and 108 can be compared in comparator 106 to yield an output bit stream (e.g., a full stream of ‘1’ values for a ‘1’ data portion, and a full stream of ‘0’ values for a ‘0’ data portion) corresponding to the ASK modulation of the input.
Integrating such a receiver into a modern digital CMOS VLSI chip can require analog components, which may either be external to the chip or occupy a relatively large area of the chip. Therefore, modern designs may utilize more complex receiver methods to permit integration onto a single chip. However, a diode peak demodulator may still require relatively large analog components, since the peak is typically detected over many cycles of the carrier wave in this approach. Thus, a demodulation approach for ASK AM modulation using primarily digital logic that can occupy a relatively small chip area would be advantageous. Further, such a digital approach would be particularly advantageous when implemented without a multi-bit analog to digital converter (ADC) for the demodulator.